Unnamed Tributary to Twelvemile Creek IA 05-GRA-6577

from mouth (T73N R30W Sec27 Union Co.) to headwaters (T73N R30W Sec15 Union Co.)

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2016 - 2018
Stream/River Water Quality Data	CY 2016 - 2018
Lake Water Quality Data	CY 2014 - 2018
Biological Sampling Data	CY 2014 - 2018*
Fish Kill Data	CY 2014 - 2018
Fish Tissue Sampling Data	CY 2014 - 2018
Continuous Dissolved Oxygen Sampling Data	CY 2014 - 2018
*Biological sites sampled in both 2013 and 2017 were also assessed.

Open Segment Map
View assessment methodology in new window

Cycle: 2020
Release Status: Final
Overall IR: 3 - Insufficient data exist to determine whether any designated uses are met.
Trend: Unknown
Created: 10/1/2020 6:59:11 AM
Updated: 10/12/2020 8:32:05 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Assessed

Class BWW1

Presumptive Use

Aquatic Life - Warm Water Type 1

WINOFI

Organic Enrichment: Low Dissolved Oxygen

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2014

Impairment Rationale

Potential Impairment

Data Source

Watershed project monitoring

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 use was assessed as “fully supported” based on limited pH monitoring data. The presumptive Class BWW1 use remains assessed as “partially supported” due to violations of dissolved oxygen criterion. This assessment is considered evaluated (of lower confidence)—and thus not appropriate for Section 303(d) listing—for two reasons:(1) the Iowa DNR IR methodology requires that at least 10 samples be collected over the three-year assessment period in order to develop a “monitored” (i.e., higher confidence) assessment that is appropriate for Section 303(d) listing and (2) all violations of dissolved oxygen criteria occurred in this headwater stream segment in the exceptionally warm and dry mid-to late summer period of 2012.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2012	13880005	Unnamed Creek at 140 St	Site 12m-5

Presumptive Class A1 - Indicator Bacteria: No Data

Presumptive Class A1 - pH

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	% Acute/ Chronic Violations	Significantly >10% Violations	Assessment Type	Support Level
13880005	6	pH	5 / 1	8.4	7.2	8	1 / NA	20% / NA	No	Evaluated	Full

Presumptive Class BWW1 - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	% Acute/ Chronic Violations	Significantly >10% Violations	Assessment Type	Support Level
13880005	6	Ammonia	4 / 1	0.5	0.18	0.08	0 / 0	0% / 0%	No	Evaluated	Full
13880005	6	Dissolved oxygen	5 / 1	8.1	4.8	5	NA / 2	NA / 40%	Yes	Evaluated	Partial
13880005	6	pH	5 / 1	8.4	7.2	8	1 / NA	20% / NA	No	Evaluated	Full
13880005	6	Temperature	5 / 1	27.7	22.2	22.4	0 / 0	0% / 0%	No	Evaluated	Full

Monitoring and Methods

Assessment Key Dates

5/10/2012

Non-fixed Monitoring Start Date

6/28/2012

Non-fixed Monitoring End Date

Methods

150

Monitoring data more than 5 years old

220

Non-fixed station physical/chemical monitoring (conventional pollutant only)